I use 87, but it depends on the bike. Some need higher octane. Especially large v-twins. But far more important is the ethanol content. Ethanol is BAD. I would gladly pay for higher octane gas if it were ethanol free. I have used 100 octane race gas in bikes to store them (it last a LOT longer than that ethanol crap) and have started them up every once in a while, they seem to run fine on it.

With the except of a tank or two while on a long ride, only non-ethanol so far - at 90 octane. Same for my boat and no water issues.

I've used the 90 on all my bikes and never had a preignition issue that I'm aware of. I've even used 87 on my old GS with no issues. That was in canada and the only fuel available. I just made sure not to push the revs too high and not lugg the motor either.

I use 87, but it depends on the bike. Some need higher octane. Especially large v-twins. But far more important is the ethanol content. Ethanol is BAD. I would gladly pay for higher octane gas if it were ethanol free. I have used 100 octane race gas in bikes to store them (it last a LOT longer than that ethanol crap) and have started them up every once in a while, they seem to run fine on it.

I'm not sure what the point of this question is? It should be based on whatever is in your owner's manual or whatever your bike is tuned for. Different bikes have different requirements. I do think it's strange how some people are afraid to put 87 in their bikes even when it's the black and white requirement in the owner's manual.

All my bikes require higher octane fuel. The off roaders get fed Sunoco EXO2 which is 107 R+M/2 octane. Used to use VP but they've made it so difficult for their dealers it became hard to find consistently. The street bikes enjoy premium (91+) fromTop Tier stations whenever possible.

Burning something with a higher rating than the engineer designed the motor to

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The Engineer tuned for. You can usually tune to run higher octane, you just have to account for the slower burn with the ignition advance. That being said, yes higher than the recommended octane level just contributes to valve/piston deposits.

The octane requirement also decreases with altitude, I could run my Speed Triple that is tuned for only 91 on 86 at 9000 feet without pinging.

The Engineer tuned for. You can usually tune to run higher octane, you just have to account for the slower burn with the ignition advance.

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I have never met an engineer who has tuned an engine so it can run higher octane gasoline. People tune engines for more power. Mods used to get more power make the engine more likely to detonate. Higher octane gas is more resistant to detonation, so it gets used. Higher octane gasoline does not add any power on it's own. Tuning dictates the octane rating, not the other way around. Along those lines, timing isn't changed to allow the use of higher octane gas, higher octane gas might be used to allow changing the timing.

Which leads to; higher octane gasoline does not control detonation by burning slower than lower octane gas. Slowing down the burn would make detonation even worse. Swirl is put into the intake charge to make the mixture burn faster. Dual plugs cause the mixture to burn faster. Burning the mixture faster is a good thing.

At a given temp and given pressure as seen in an engine, you've got a finite amount of time before the mixture goes bang with no help from a flame front. Call it the delay period. The mixture has to burn fast enough that there's nothing left to explode when the delay period runs out. (Unless of course you're running a diesel, in which case you want to exploit this compression ignition stuff)

Raising compression shortens this delay period, leading to issues with detonation. To avoid this, you need to burn the mixture faster or make the delay period longer. The mixture can be made to burn faster by adding another plug. Or by adding swirl to the mix, exposing the flame front to the mixture faster than just letting it burn on it's own. The delay period can be made longer by raising the octane, or by lowering the temperature. Any combination of these things (and more) help avoid detonation caused by higher compression. Point being that lowering flame speed goes counter to other mods that are done.

Slowing down the burn to avoid detonation makes no sense, detonation is not a result of the flame front moving too quickly, it's the result of the mixture being exposed to high temp and pressure for too long so it explodes. Burning quickly is good. Exploding is bad. Flame fronts do not speed up to the point of an explosion.